I'd advise you to first learn and understand what it is you're trying to do;
https://crackstation.net/hashing-security.htm[
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The above link has c# examples, and there are other examples too if you google "c# hash passwords with salt".
Second of all you're passing the result of a bool function (IsPasswordValue) to your SQL so your SQL is going to be
select * from tb_employees where emp_email = 'me@here.com' and emp_password = true
I'm going to assume your emp_password field contains the hashed\encrypted password and not just true or false. When the user creates their account you generate the hashed version of their password (including the salt). You save the hashed password as well as the salt that was used in the database against that user. When they login you retrieve their hashed password and their salt, you then re-hash the password they supplied in the password box with the salt you retrieved from the database, and see if that matches the hashed password you retrieved from the database. If they match the person has logged in.